Ventricular tachycardia (VT) and fibrillation (VF) are a major cause of sudden cardiac death (SCD) in those with coronary artery disease (CAD). The source of VT/VF is believed to be the arrhythmogenic substrate within scarred myocardium, creating areas prone to reentrant ventricular tachyarrhythmia. Late gadolinium enhancement (LGE) cardiovascular MR (CMR) is the non-invasive gold standard for in-vivo identification of myocardial scar, but its clinical value in treatment or risk stratifying VT patients remains uncertain. LGE CMR has been employed to identify areas which contain a mixture of living cells and fibrosis (tissue heterogeneity), called the 'grey zone'(GZ) (a.k.a. 'peri-infarct zone'or 'arrhythmic border zone'). Numerous studies have shown that the volume of GZ, much more powerfully than the volume of scar, predicts inducibility of VT and arrhythmic death. Our hypothesis is that more accurate identification of GZ is possible, and will increase the power of LGE to predict arrhythmia, risk-stratify for SCD, and identify the arrhythmic border zone for VT ablation. We propose using high spatial resolution LGE to resolve complex scar morphology, and T1- mapping for quantitative identification of GZ. Reverse-contrast LGE, by which GZ is bright and scar is dark, highlights GZ within the scar core. The CMR methods to better classify GZ will be applied to an animal study for histopathological correlation, and a pilot study of VT patients. PUBLIC HEALTH RELEVANCE: Ventricular tachycardia is a common arrhythmia, responsible for almost half of deaths due to heart-disease. The cause of the arrhythmia is often scar in the heart muscle after a heart-attack, which changes the electrical signals within the heart. We will study ways to use cardiac MRI to detect scar in the heart which may result in an arrhythmia.